In a third generation partnership project (3GPP) Release 6 (R6) system, the Radio Link Control (RLC) layer in acknowledged mode (AM) operates using fixed protocol data unit (PDU) sizes. In addition, the medium access control high speed (MAC-hs) layer in the base station and the medium access control (MAC) in the wireless transmit/receive unit (WTRU) do not support segmentation of service data units (SDUs) from higher layers. These restrictions may result in performance limitations, especially as high speed packet access (HSPA) evolves towards higher data rates.
In order to achieve higher data rates and reduce protocol overhead and padding, a number of new features to the layer 2 (L2) protocol were introduced in Release 7 of the 3GPP specifications. Flexible RLC PDU sizes and MAC segmentation in the downlink were among the concepts introduced. It has also been proposed to enhance L2 operation in the uplink. Some enhancements that have been proposed are directed toward, for example: introducing support for flexible RLC PDU sizes, introducing support for MAC segmentation, allowing for smooth transition between old and new protocol formats, and supporting seamless state transitions between CELL_DCH, CELL_FACH, CELL_PCH and URA_PCH, (e.g., dependent on potential enhancements to the CELL_FACH UL transmission).
FIG. 1 shows a conventional protocol architecture 100, (e.g., with MAC layer and below) with the use of an enhanced dedicated channel (E-DCH), such as described in Release 7 of the 3GPP specifications. The MAC sub-layers specific to the use of E-DCH are the MAC-es and MAC-e sublayers. Potentially, improvements to L2 protocols could be achieved by enhancing the RLC sub-layer (not shown in FIG. 1), the MAC-es and the MAC-e sub-layers. It should be noted that only the MAC-e sub-layer is terminated in the base station.
The improved L2 enhanced MAC-e/es entity may be referred to as a MAC-i-is entity. The improved L2 features can be used for E-DCH transmission in CELL_DCH or for E-DCH transmission in CELL_FACH. The latter is also referred to as E-RACH transmission.
Since the deployment of a new feature such as improved uplink (UL) Layer 2 protocols in a system usually cannot be performed in the whole system at the same time, for a period of time there will be areas covered by base stations that do not support the new feature. This may be the case even if these base stations are part of a radio network subsystem controlled by a radio network controller (RNC) supporting the new feature. As these legacy base stations will be adjacent to base stations implementing the new feature (“enhanced base stations”), there will be WTRUs starting their communications within the area covered by enhanced base stations and moving within an area covered by legacy base stations.
It would therefore be beneficial to provide a method and apparatus to support uplink protocols in the area covered by enhanced base stations while providing a smooth transition as a WTRU moves into an area covered by legacy base stations.